docs: def hourly_horizontal_infrared(self):
          """A data collection containing hourly horizontal infrared intensity in W/m2.
          """
          sky_cover = self._sky_condition.hourly_sky_cover
          db_temp = self._dry_bulb_condition.hourly_values
          dp_temp = self._humidity_condition.hourly_dew_point_values(
              self._dry_bulb_condition)
  
          horiz_ir = []
          for i in xrange(len(sky_cover)):
              horiz_ir.append(
                  calc_horizontal_infrared(sky_cover[i], db_temp[i], dp_temp[i]))
  
          return self._get_daily_data_collections(
              energyflux.HorizontalInfraredRadiationIntensity(), 'W/m2', horiz_ir)